A capacitive MEMS pressure sensor requires two electrodes that move relative to each other under an applied pressure. This is most often accomplished by having a fixed electrode (hereafter called the lower electrode) formed in a substrate while a moveable electrode (hereafter called the upper electrode) is provided in a deformable membrane which is exposed to the pressure that is to be sensed. One or more of the electrodes are typically formed by deposition of a conductive film, electrical isolation of a conductive layer, or by simply adding a spacer layer between two conductive materials.
While known methods of forming electrodes are effective, such electrodes may introduce undesired properties or process steps into a device. By way of example, deposition of material requires additional process steps thereby complicating manufacturing processes. Moreover, use of different materials can result in undesired stress at the material junction, thermal mismatch in materials, etc.
Additionally, when an electrode is formed by deposition, an electrically isolated lower layer is required such as may be provided by a silicon-on-insulator (SOI) wafer or the like. Providing such isolated lower layers increases device complexity including the need for additional materials and processing steps. Moreover, devices incorporating deposited electrodes may exhibit reduced electrical isolation which leads to increased feedthrough capacitance and reduced shielding, thereby reducing the performance of the final sensor.
What is needed therefore is a simple and reliable device with an out-of-plane electrode and method for producing the device. A device incorporating an out-of-plane electrode that is easily fabricated with an encapsulated vacuum would be further beneficial.